Spreading dynamics and sedimentary process of the Southwest Sub-basin, South China Sea: Constraints from multi-channel seismic data and IODP Expedition 349

© 2015 The Authors. Neotectonic and sedimentary processes in the South China Sea abyssal basin are still debated because of the lack of drilling evidence to test competing models. In this study, we interpreted four multi-channel seismic profiles across the Southwest Sub-basin (SWSB) and achieved stratigraphic correlation with new drilling data from Integrated Ocean Discovery Program (IODP) Expedition 349. Neogene sediments are divided into four stratigraphic units, each with distinctive seismic character. Sedimentation rate and lithology variations suggest climate-controlled sedimentation. In the late Miocene winter monsoon strength and increased aridity in the limited accumulation rates in the SWSB. Since the Pliocene summer monsoons and a variable glacial-interglacial climate since have enhanced accumulation rates. Terrigeneous sediments in the SWSB are most likely derived from the southwest. Three basement domains are classified with different sedimentary architectures and basement structures, including hyper-stretched crust, exhumed subcontinental mantle, and steady state oceanic crust. The SWSB has an asymmetric geometry and experienced detachment faulting in the final stage of continental rifting and exhumation of continental mantle lithosphere. Mantle lithospheric breakup post-dates crustal separation, delaying the establishment of oceanic spreading and steady state crust production

Emergency Management System for Sudden Water Pollution Accidents

The emergency management system for sudden water pollution accidents of the main canal is the integrated application of the aforesaid three key technologies and is the key to verify the effect of practical application of these technologies. The emergency management system is formed by integrating basic information, measured data, and professional models through the communication mode of network transmission. The system can provide support for emergency response in case of emergency conditions including sudden water pollution accidents and technical support for security operations of the MRP

Potassic Volcanism Induced by Mantle Upwelling through a Slab Window: Evidence from Shear Wave Splitting Analyses in Central Java

To delineate the mantle flow fields in the vicinity of a previously proposed slab window and the possible roles that they may play in the formation of potassic volcanism in Central Java, we conduct shear wave splitting analyses using both local S and teleseismic XKS waves (including SKS, SKKS, and PKS) recorded by 121 onshore stations and two ocean bottom seismometers (OBSs). The XKS fast orientations from the OBSs are trench normal and in accord with previous subslab anisotropy measurements. In the eastern part of Central Java, the XKS and local S fast orientations from the onshore stations are mostly trench-parallel; in contrast, in the western part of Central Java, the XKS fast orientations are trench-normal while the local S measurements are spatially varying. The observations can be attributed to four flow systems including (a) subslab trench normal mantle flow in areas away from the trench which is entrained by the Australian Plate, (b) trench normal flow that goes into the mantle wedge from the subslab area through a slab window beneath the western part of the study area, (c) trench-parallel subslab flow near the trench beneath the eastern part of the study area which is driven by slab-rollback, and (d) dominantly trench-parallel flow system in the mantle wedge reflecting the horizontal component of the escaped flow system through the slab window. We propose that the vertical component of the escaped flow is responsible for the formation of the potassic volcanoes in the adjacent oceanic area

Slab Dehydration and Mantle Upwelling in the Vicinity of the Sumatra Subduction Zone: Evidence from Receiver Function Imaging of Mantle Transition Zone Discontinuities

A total of 10,586 P-to-S radial receiver functions recorded by 64 broadband seismic stations were utilized to image the 410 and 660 km discontinuities (d410 and d660, respectively) bordering the mantle transition zone (MTZ) beneath the Sumatra Island, the Malay Peninsula, and the western margin of the South China Sea. The d410 and d660 were imaged by stacking receiver functions in successive circular bins with a radius of 1°, after moveout corrections based on the 1-D IASP91 Earth model. The resulting apparent depths of the discontinuities exhibit significant and spatially systematic variations. The apparent depths of the d410 and d660 range from 382 to 459 km and 637 to 700 km with an average of 406 ± 13 and 670 ± 12 km, respectively, while the corresponding values for the MTZ thickness are 217 to 295 km and 261 ± 13 km. Underneath southern Sumatra and adjacent regions, the MTZ is characterized by an uplifted d410 and a depressed d660. While the former is probably caused by the low temperature anomaly, the latter is most likely related to a combination of the low temperature anomaly and dehydration associated with the subducted Australian Plate that has reached at least the d660. In contrast, an abnormally thin MTZ is imaged to the southwest of the Toba Caldera. This observation, when combined with results from previous seismic tomography studies, can be explained by advective thermal upwelling through a slab window

Geodynamic effects of subducted seamount at the Manila Trench: Insights from numerical modeling

Abstract We used numerical modeling to investigate the geodynamic effects of subducted seamounts at the Manila Trench. A series of numerical modeling experiments were conducted with variable parameters, including the activation volume (Vact) and cohesion (C), which influence lithospheric rheology, the plate convergence velocity, and the age of subducting slab. Modeling results indicate that varying the Vact and C within an appropriate range have limited effects on the geodynamic process of subduction. A lower Vact allows the slab to sink more easily and results in a steeper dip angle. A slab break-off is more likely to occur under subduction at depths of 100–300 km, while the existence of a seamount further promotes the break-off process. The convergence rate is a key parameter affecting the break-off timing and depth. In contrast, under subduction where subducted oceanic plate move faster upper plate, the model results exhibit non-break-off, steady subduction. Slab age is another factor controlling break-off, where break-off time extends with slab age. A subduction without seamount will cause a ~2 Myr delay in break-off timing. We suggest that the low-velocity zone under the Manila Trench at 17o N is the result of a break-off event due to subduction of the Zhenbei-Huangyan Seamount Chain. Further to the north, such as the location at 19o N, the absence of seamount and an older oceanic crust would favor a delay in break-off timing during subduction

Metastable Olivine within Oceanic Lithosphere in the Uppermost Lower Mantle Beneath the Eastern United States

Approximately two-thirds of Earth\u27s outermost shell is composed of oceanic plates that form at spreading ridges and recycle back to Earth\u27s interior in subduction zones. A series of physical and chemical changes occur in the subducting lithospheric slab as the temperature and pressure increase with depth. In particular, olivine, the most abundant mineral in the upper mantle, progressively transforms to its high-pressure polymorphs near the mantle transition zone, which is bounded by the 410 km and 660 km discontinuities. However, whether olivine still exists in the core of slabs once they penetrate the 660 km discontinuity remains debated. Based on SKS and SKKS shear-wave differential splitting times, we report new evidence that reveals the presence of metastable olivine in the uppermost lower mantle within the ancient Farallon plate beneath the eastern United States. We estimate that the low-density olivine layer in the subducted Farallon slab may compensate the high density of the rest of the slab associated with the low temperature, leading to neutral buoyancy and preventing further sinking of the slab into the deeper part of the lower mantle